THESSALONIKI — Greek authorities said Thursday that they have rescued nine men from Pakistan who were being held for ransom in the northern city of Thessaloniki and arrested another three — also Pakistanis — as their suspected kidnappers.

Police said authorities were first alerted to the case on Monday by two men on the island of Lesbos who reported to police there that their 50-year-old brother had been abducted by kidnappers demanding 2,000 euros ($2,300) for his release.

An investigation determined the man was being held in Thessaloniki, and an operation was set up to deliver the ransom on Tuesday evening, police said. Authorities arrested a 27-year-old man when he turned up with the victim at the designated spot near a train station and received the cash.

Following further investigation, police raided several apartments, from which they freed another eight kidnapped men, and arrested two suspected kidnappers, aged 24 and 20. The kidnappers had allegedly been holding the victims for ransoms ranging from 1,000 to 2,000 euros.

The three suspects face charges of kidnapping, blackmail and attempted blackmail, and are to appear before a prosecutor in Thessaloniki.

The northern Greek city is on a migration route for people fleeing poverty and conflict in Asia, Africa and the Middle East, with smugglers guiding them across Greece’s northeastern land border with Turkey and then driving them to Thessaloniki. From there, many hope to head north through the Balkans toward more prosperous European countries.